1. Field
The present disclosure relates to film deposition techniques, and more particularly, to metal chalcogenide film deposition techniques. For instance, metal chalcogenide film deposition techniques may be applied to the fabrication of semiconductor devices, solar cells, light-emitting diodes, etc.
2. Description of the Related Art
In the formation of semiconductor films, a vapor deposition process such as chemical vapor deposition, physical vapor deposition, or sputtering is generally used. If a vapor deposition process can be replaced with a liquid deposition process, the coasts associated with equipment, facilities, processes, and energy may be significantly reduced because the liquid deposition process may be performed by an inexpensive coating method such as a spin coating method.
Liquid deposition processes may require a precursor in a liquid form. However, inorganic substances such as metal chalcogenide compounds are not dissolved well in most solvents.
An approach of preparing a precursor solution using organometallic compounds which are soluble in solvents may be considered. However, if a precursor solution including organometallic compounds is employed to form an inorganic films, it is necessary to remove organic moieties from precursor films formed from the organometallic compounds. Organic moieties may be decomposed or evaporated by heating the precursor films at temperatures of about 500° C. or higher. However, such an organic moiety removal process results in the formation of porous inorganic films instead of dense inorganic films. Moreover, the organic moiety removal process leaves carbon residue on the inorganic films. The carbon residue may adversely affect electrical properties of the inorganic films.
Thus, a precursor solution containing inorganic compounds which is free of problems associated with the use of organometallic compounds are still desired.
It has recently been suggested to use hydrazine, to which Te2+ ions are added, as a solution for preparing a precursor solution containing ZnTe as a metal chalcogenide compound. Solution Processing of Chalcogenide Semiconductors Via Dimensional Reduction, David B. Mitzi, Adv. Mater. 2009, 21, 3141-3158.
Te2+ ion-containing hydrazine may be prepared by injecting metal tellurium (Te) into hydrazine. The metal Te is converted into Te2+ ions in hydrazine to form a “Te2+-hydrazine solvent system.” Hydrazine alone may not dissolve ZnTe bulk powder. However, the “Te2+-hydrazine solvent system” may effectively dissolve ZnTe bulk particles through a dimension reduction mechanism. The ZnTe bulk particles may be illustrated as a three-dimensional copolymer. Te2+ ions in hydrazine attack and break a bond between zinc (Zn) and Te. Accordingly, the ZnTe bulk particles are divided and converted into a solute having a size of monomer (Zn—Te) or cluster including two to several hundreds of “—Zn—Te—” units.
However, hydrazine is poisonous and may be explosive. Using hydrazine in the ambient atmosphere raises many technical issues. Therefore, there are many limits to using precursor solutions including hydrazine as a solvent in industrial applications. Unlike hydrazine, hydrazine derivatives, hydrazine hydrates, or hydrazine derivative hydrates are not explosive at ambient atmosphere.
In order to dissolve metal chalcogenide compounds through dimension reduction mechanisms, ions of a chalcogen element are included in the solvent system. However, the ionization of the chalcogen element does not occur in non-explosive hydrazine-based solvents such as hydrazine hydrates, hydrazine derivatives, hydrazine derivative hydrates, etc. Accordingly, metal chalcogenide compound solutions containing the non-explosive hydrazine-based solvents as solvents do not exist.